AB0164 SERUM LEVELS OF INTERLEUKIN-36 Α TO DISTINGUISH BEHÇET’S SYNDROME AND PSORIATIC ARTHRITIS
Authors: A. Bettiol, F. Fagni, I. Mattioli, G. Bagni, G. Vitiello, A. Grassi, C. Della Bella, M. Benagiano, A. Troilo, K. S. Holownia, D. Simon, F. R. Argento, J. Sota, C. Fabiani, M. Becatti, C. Fiorillo, G. Schett, G. Lopalco, L. Cantarini, D. Prisco, E. Silvestri, G. Emmi, M. M. D’elios
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Behçet's syndrome (BS) is a rare systemic vasculitis hallmarked by oral, genital and ocular involvement, often accompanied by articular, cutaneous, vascular, neurological, and gastrointestinal manifestations [1, 2]. Articular involvement is present in up to 80% of BS patients [3], and, from a clinical point of view, it may resemble seronegative arthritis, particularly psoriatic arthritis (PsA), with which an overlap has also been described [4-6]. To this date, no specific instrumental or laboratory biomarker is available to help the differential diagnosis between BS and PsA, which currently relies only on clinical assessment and might be particularly challenging. On these bases, there is a growing interest on the identification of new laboratory biomarkers which might assist in the diagnostic process. Among them, interleukin (IL)-36 belongs to the IL-1 family and is involved in skin and joint-related inflammatory conditions [7, 8]. Increased serum levels of IL-36, especially IL-36α, have been described in PsA at synovial level [9], while no study investigated its levels in BS. <h3>Objectives</h3> This study aimed to assess the ability of serum IL-36α to differentiate BS from PsA patients. <h3>Methods</h3> A cross-sectional study was performed on a cohort of 90 adult patients with BS followed at two referral centres for BS (Behçet Center of the Careggi University Hospital of Florence, and University Hospital of Siena, Italy), 80 patients with PsA from the University Hospital Erlangen (Germany), and 80 healthy controls (HCs). Serum IL-36α concentrations were measured in blood samples using human IL-36α enzyme-linked immunosorbent assay (ELISA) kits (MyBioSource, San Diego, Ca), and compared in the three groups. <h3>Results</h3> Serum IL-36α concentrations were significantly higher among BS patients [median level of 201.7 (112.7 – 320.2) pg/mL] as compared to HC [16.9 (13.7-22.2); p&lt;0.001]. Conversely, BS patients displayed significantly lower IL-36α levels as compared to the PsA group (544 (296-759); p&lt;0.001) (<b>Figure 1</b>). When we investigated the ability of IL-36α to discriminate BS patients from PsA patients, an empirical optimal cut-off of 420.6 pg/ml displayed a specificity of 0.93, with a sensitivity of 0.70 (AUC 0.82) in discriminating PsA from BS. This cut-off displayed a good diagnostic performance also in BS patients with mucosal and ocular manifestations, i.e., the two BS involvement associated with the highest IL-36α levels, as well as in those lacking major organ involvement, who represent a challenging group from a diagnostic point of view. <h3>Conclusion</h3> Serum IL-36α is remarkably increased in patients with PsA as well as in BS, although to a lesser extent. Serum IL-36α could be a candidate biomarker for the differential diagnosis between these two conditions. <h3>References</h3> [1] Bettiol A, Front Immunol. 2019. [2] Bettiol A, Rheumatology (Oxford). 2020 [3] Tursen U, Int J Dermatol. 2003 [4] International Team for the Revision of the International Criteria for Behcet's Disease, J Eur Acad Dermatol Venereol. 2014;28(3):338-47. [5] Di Scala G, J Autoimmun. 2019 [6] Fagni F, Ann Rheum Dis. 2020 [7] Magne D, Arthritis Res Ther. 2006. [8] Boutet MA, Clin Exp Immunol. 2016. [9] Boutet MA, Rheumatology (Oxford). 2020. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.